1. Technical Field
The inventions relate to electronic amplifiers and methods of operating electronic amplifiers.
2. Discussion of the Related Art
This section introduces aspects that may be helpful to facilitating a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.
FIG. 1 illustrates an exemplary light detection circuit 10 that is based on a differential active transimpedance amplifier (ATIA) 12 and a matched pair of reverse-biased photodiodes 14, 16. The light detection circuit 10 measures differences in intensities of light L1, L2 incident on the two photodiodes 14, 16. In particular, the first and second photodiodes 14, 16 produce respective first and second output currents I1, I2. The magnitude of the first output current I1 and the second output current I2 indicate the intensity of the light L1, L2 incident on the respective first photodiode 14 and the second photodiode 16.
The differential ATIA 12 is a current-to-voltage converter. For that reason, the difference between the voltages at the first and second outputs of the differential ATIA 12 are about proportional to the difference between the currents I1, I2 that are applied to the first and second inputs of the ATIA.
The differential ATIA 12 includes an electronic differential amplifier 18 and first and second electrical feedback lines 20, 22. The inverting electronic differential amplifier 18 may have a high input impedance, a low output impedance, and a high voltage gain, e.g., as an operational amplifier. Each electrical feedback line 20, 22 includes a resistor R. Each electrical feedback line 20, 22 connects one of the outputs 24, 26 of the electronic differential amplifier 18 to a corresponding one of the inputs 28, 30 of the electronic differential amplifier 18 in a voltage-inverting manner. Thus, the electrical feedback lines 20, 22 produce negative feedback that can stabilize the operation of the electronic differential amplifier 18. In addition, the resistors R are passive internal loads that enable the currents input to the ATIA 12 to produce output voltages. For that reason, the ATIA 12 functions as a current-to-voltage converter.
Each photodiode 14, 16 has an output that connects to one of the inputs 28, 30 of the ATIA 12. For that reason, the ATIA 12 can produce two voltages whose difference is indicative of the difference between currents produced by the two photodiodes 14, 16. Since the magnitudes of these currents are also indicative of the intensities of the light L1, L2 received by the photodiodes 14, 16, the difference between the voltages at the two outputs 24, 26 of the electronic differential amplifier 18 can provide a measure of the difference between the intensities of the light L1, L2 received at the two photodiodes 14, 16.